Difference between 'Bounding Box center' and 'median point' pivot?
for the second question :


the bounding box center is not the same as median center :

-The Median center is calculated as the average of all selected points ( vertices or object centers ) so it depends on the density distribution of the mesh 

-The bounding box : is the smallest box (Cube ) that can contain the mesh of an object while aligned to the local space 

-The bounding Box center will always be at the center of this bounding box regardless of the density distribution of the mesh inside